As a method of diagnosing breast cancer, cirrhosis, vascular disease and the like, there has been known a method (an elastography technology) of diagnosing hardness in a subject such as a living body from an ultrasonic echo signal, instead of palpation of a doctor. When diagnosing the hardness of the subject by the elastography technology, an engaged person touches and presses an ultrasonic probe to a surface of the subject, thereby generating a displacement in a tissue in the subject. Before and after compression of the internal tissue by the pressing, an ultrasonic beam for displacement detection is irradiated to acquire an echo signal, a displacement in the compression direction is estimated on the basis of the acquired echo signal and a distortion, which is a spatial differentiating amount of the displacement, is calculated. Further, a value relating to the hardness, for example, a Young's modulus is calculated from the distortion and stress. Also, as disclosed in NPL 1, there is an elastography technology of using a focused beam of ultrasonic waves to apply a radiation pressure into a subject, displacing a target tissue while suppressing an influence of an interposed layer, irradiating an ultrasonic beam for displacement detection to acquire an echo signal, and diagnosing hardness of the subject such as a living body on the basis of the acquired echo signal.